1. Field of the Invention
The invention relates to a projection display, more particularly to a projection display with two reflective light valves.
2. Description of the Related Art
In a conventional projection display, primary color components, such as red, green and blue color components, are processed before projecting the same so as to form an image on a projection screen. During the processing of light, the issue of light leakage must be addressed in order to achieve optimum image quality.
Referring to FIG. 1, a conventional projection display 1 is shown to comprise a polarization beam splitter prism 11 which reflects S-polarization light in a transverse direction and which allows P-polarization light to pass directly therethrough. The polarization beam splitter prism 11 has a light input side 111, a first split-light side 112 adjacent to the light input side 111, a second split-light side 113 opposite to the light input side 111, and a light output side 114 opposite to the first split-light side 112. A P-state polarizer 12 is disposed adjacent to the light input side 111, allows P-polarization light to pass directly therethrough, and absorbs S-polarization light. A first light polarization selector 13 is disposed between the P-state polarizer 12 and the light input side 111, and converts the polarization state of red light that passes therethrough. A first reflective light valve 14 is disposed adjacent to the first split-light side 112, whereas a second reflective light valve 15 is disposed adjacent to the second split-light side 113. A color switch 16 is disposed between the second split-light side 113 and the second reflective light valve 15, and allows color components to pass therethrough in accordance with a predetermined color sequence. A second light polarization selector 17 is disposed adjacent to the light output side 114. An S-state polarizer 18 is disposed adjacent to one side of the second light polarization selector 17 opposite to the light output side 114, and prevents P-polarization light from passing therethrough. A projection lens 19 receives the light that passes through the S-state polarizer 18. When the first and second reflective light valves 14, 15 are in an active (ON) state, they modulate and convert the polarization state of light that is incident thereon, and reflect the modulated light in an opposite direction. In the following paragraphs, the operation of the conventional projection display 1 will be described in greater detail with the first and second reflective light valves 14, 15 in the active (ON) state. In addition, each of a pair of quarter wavelength plates is disposed between the polarization beam splitter prism 11 and a respective one of the first and second reflective light valves 14, 15 for enhancing the image contrast quality.
In use, when input white light 10 is provided to the P-state polarizer 12, only P-polarization first, second and third color components 101, 102, 103 (such as red, blue and green color components) will pass therethrough and reach the first light polarization selector 13. The first light polarization selector 13 changes the polarization state of the first color component 101 to S-polarization, and maintains the polarization state of the second and third color components 102, 103 at P-polarization. When the polarization beam splitter prism 11 receives the first, second and third color components 101, 102, 103 from the first light polarization selector 13, the S-polarization first color component 101 will be reflected toward the first reflective light valve 14, whereas the P-polarization second and third color components 102, 103 will be allowed to pass directly through the polarization beam splitter prism 11. The second and third color components 102, 103 from the polarization beam splitter prism 11 will be controlled by the color switch 16 so as to pass sequentially therethrough and reach the second reflective light valve 15. Because the paths of the second and third color components 102, 103 and the processing procedure therefor are essentially the same, processing of the third color component 103 will not be described herein for the sake of brevity.
When the first and second reflective light valves 14, 15 are in the active (ON) state, the S-polarization first color component 101 will be modulated by the first reflective light valve 14, and the polarization state of the first color component 101 will be changed to P-polarization. The P-polarization first color component 101 will then be reflected by the first reflective light valve 14 back to the polarization beam splitter prism 11, and will be allowed by the polarization beam splitter prism 11 to pass directly therethrough so as to reach the second light polarization selector 17. The second light polarization selector 17 will convert the polarization state of the P-polarization first color component 101 to S-polarization, and the S-polarization first color component 101 will pass through the S-state polarizer 18 before reaching the projection lens 19 for projecting the same on a projection screen (not shown). On the other hand, the P-polarization second color component 102 will be modulated by the second reflective light valve 15, and the polarization state of the P-polarization second color component 102 will be changed to S-polarization. The S-polarization second color component 102 will then be reflected by the second reflective light valve 15 back to the polarization beam splitter prism 11, and will be further reflected by the polarization beam splitter prism 11 to pass in sequence through the second light polarization selector 17 and the S-state polarizer 18 so as to reach the projection lens 19. When the second color component 102 is projected by the projection lens 19, it cooperates with the first color component 101 to form an image on the projection screen (not shown).
In the aforesaid conventional projection display 1, white light is separated into color components, which are modulated by reflective light valves and which are subsequently recombined to form images on a projection screen. However, due to current manufacturing constraints and the characteristics of polarized light, P-polarization light will be unable to pass through the polarization beam splitter prism with very high transmission efficiency. As such, when P-polarization light passes directly through the polarization beam splitter prism, a small portion of the P-polarization light will be reflected to form light leakage components, as indicated by the phantom lines in FIG. 1. While a portion of the S-polarization light will pass through the polarization beam splitter prism to result in corresponding light leakage components, the amount of the light leakage components attributed to the S-polarization light is much less than that attributed to the P-polarization light. In the conventional projection display 1 of FIG. 1, it is assumed that 10% of the P-polarization light will be reflected by the polarization beam splitter prism 11 to form light leakage components, and that 2% of the S-polarization light will be allowed by the polarization beam splitter prism 11 to pass directly therethrough to form light leakage components. Therefore, when the S-polarization first color component 101 is reflected by the polarization beam splitter prism 11, about 2% of the first color component 101 will form a first light leakage component 101xe2x80x2 that passes directly through the polarization beam splitter prism 11 and that reaches the second reflective light valve 15. The second reflective light valve 15 will change the polarization state of the first light leakage component 101xe2x80x2 to P-polarization, and the P-polarization first light leakage component 101xe2x80x2 will be reflected back to the polarization beam splitter prism 11. At this time, about 10% of the P-polarization first light leakage component 101xe2x80x2 will be reflected by the polarization beam splitter prism 11 to form another light leakage component 101xe2x80x3 that passes through the second light polarization selector 17 and the S-state polarizer 18 before reaching the projection lens 19. Thus, the amount of light leakage component received by the projection lens 19 and attributed to the first color component 101 is equal to 0.02xc3x970.1 or 0.2%. Accordingly, when the P-polarization second color component 102 passes directly through the polarization beam splitter prism 11, about 10% of the second color component 102 will form a second light leakage component 102xe2x80x2 that is reflected by the polarization beam splitter prism 11 and that reaches the first reflective light valve 14. The first reflective light valve 14 will change the polarization state of the second light leakage component 102xe2x80x2 to S-polarization, and the S-polarization second light leakage component 102xe2x80x2 will be reflected back to the polarization beam splitter prism 11. At this time, while about 98% of the S-polarization second light leakage component 102xe2x80x2 will be reflected by the polarization beam splitter prism 11 toward the first light polarization selector 13, about 2% of the S-polarization second light leakage component 102xe2x80x2 will be allowed by the polarization beam splitter prism 11 to pass directly therethrough to form yet another light leakage component 102xe2x80x3 that passes through the second light polarization selector 17 and the S-state polarizer 18 before reaching the projection lens 19. Thus, the amount of light leakage component received by the projection lens 19 and attributed to the second color component 102 is equal to 0.02xc3x970.1 or 0.2%. The large amount of light leakage components received by the projection lens 19 has a serious adverse affect on the image shown by the conventional projection display 1.
Therefore, the main object of the present invention is to provide a projection display of the type having two reflective light valves which can minimize the amount of light leakage components that reach a projection lens to achieve optimum image quality.
According to the present invention, a projection display comprises:
a polarization beam splitter prism having a light input side, a first split-light side adjacent to the light input side, a second split-light side opposite to the light input side, and a light output side opposite to the first split-light side, the polarization beam splitter prism allowing light that enters the light input side and that has a first polarization state to be reflected so as to pass through the first split-light side, and further allowing light that enters the light input side and that has a second polarization state to pass directly through the second split-light side;
a first light polarization selector disposed adjacent to the light input side, the first light polarization selector being adapted to receive an input light beam that contains first, second and third color components and to process the input light beam such that the first color component has a polarization state different from that of the second and third color components;
a projection lens disposed adjacent to the light output side;
a second light polarization selector disposed between the light output side and the projection lens, the second light polarization selector receiving light that exits the light output side and processing the light from the light output side such that the first, second and third color components thereof have the same polarization state prior to reaching the projection lens;
first and second reflective light valves disposed adjacent to the first and second split-light sides, respectively, the first reflective light valve being operable so as to modulate the first color component from the polarization beam splitter prism, the second reflective light valve being operable so as to modulate the second and third color components from the polarization beam splitter prism;
a first dichroic beam splitter disposed between the polarization beam splitter prism and the first reflective light valve for directing the first color component from the polarization beam splitter prism to the first reflective light valve, and for directing the first color component from the first reflective light valve back to the polarization beam splitter prism;
a second dichroic beam splitter disposed between the polarization beam splitter prism and the second reflective light valve for directing the second and third color components from the polarization beam splitter prism to the second reflective light valve, and for directing the second and third color components from the second reflective light valve back to the polarization beam splitter prism; and
a color switch disposed between the polarization beam splitter prism and the second reflective light valve and operable so as to allow the color components to pass sequentially therethrough.